Cytokine expression and secretion by skeletal muscle cells: regulatory mechanisms and exercise effects.

TLDR

Cytokines regulate metabolism, muscle growth, and disease, and exercise alters their production, yet the muscle‑specific release patterns and underlying mechanisms remain poorly understood. This review aims to clarify how skeletal muscle cells produce cytokines, identify other cellular sources during exercise, and examine the soluble factors and signaling pathways that regulate their synthesis. The authors review evidence on muscle cytokine production, evaluate alternative cellular contributors, and analyze regulatory mechanisms such as RNA‑binding proteins, microRNAs, SOCS proteins, and soluble receptors. Exercise induces substantial rises in circulating IL‑6, IL‑8, IL‑10, IL‑1RA, and G‑CSF, with modest elevations of TNF‑α, MCP‑1, IL‑1β, BDNF, IL‑12p35/p40, and IL‑15.

Abstract

Cytokines are important mediators of various aspects of health and disease, including appetite, glucose and lipid metabolism, insulin sensitivity, skeletal muscle hypertrophy and atrophy. Over the past decade or so, considerable attention has focused on the potential for regular exercise to counteract a range of disease states by modulating cytokine production. Exercise stimulates moderate to large increases in the circulating concentrations of interleukin (IL)-6, IL-8, IL- 10, IL-1 receptor antagonist, granulocyte-colony stimulating factor, and smaller increases in tumor necrosis factor-α, monocyte chemotactic protein-1, IL-1β, brain-derived neurotrophic factor, IL-12p35/p40 and IL-15. Although many of these cytokines are also expressed in skeletal muscle, not all are released from skeletal muscle into the circulation during exercise. Conversely, some cytokines that are present in the circulation are not expressed in skeletal muscle after exercise. The reasons for these discrepant cytokine responses to exercise are unclear. In this review, we address these uncertainties by summarizing the capacity of skeletal muscle cells to produce cytokines, analyzing other potential cellular sources of circulating cytokines during exercise, and discussing the soluble factors and intracellular signaling pathways that regulate cytokine synthesis (e.g., RNA-binding proteins, microRNAs, suppressor of cytokine signaling proteins, soluble receptors).